A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and fuel such as hydrogen, or a hydrocarbon-based material such as methanol, ethanol, natural gas, and the like.
The polymer electrolyte membrane fuel cell is a clean energy source that is capable of replacing fossil fuels. It has advantages such as high power output density and energy conversion efficiency, operability at room temperature, and being small-sized and tightly sealed. Therefore, it can be applicable to a wide array of fields such as non-polluting automobiles, and electricity generation systems and portable power sources for mobile equipment, military equipment, and the like.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC).
The direct oxidation fuel cell includes a direct methanol fuel cell that uses methanol as fuel.
The polymer electrolyte membrane fuel cell has an advantage of a high energy density and high power, but also has problems in the need to carefully handle hydrogen gas and the requirement of additional devices such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like in order to produce hydrogen as the fuel gas.
On the contrary, a direct oxidation fuel cell has a lower energy density than that of the gas-type fuel cell but has the advantages of easy handling of the liquid-type fuel, a low operation temperature, and no need for additional fuel reforming processors. Therefore, it has been acknowledged as an appropriate system for a portable power source for small and common electrical equipment.
In the above-mentioned fuel cells, a stack that generates electricity includes several to scores of unit cells stacked adjacent to one another, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate).
The membrane-electrode assembly is composed of an anode (also referred to as a “fuel electrode” or an “oxidation electrode”) and a cathode (also referred to as an “air electrode” or a “reduction electrode”) that are separated by a polymer electrolyte membrane.
Fuel is supplied to an anode and adsorbed on catalysts of the anode, and the fuel is oxidized to produce protons and electrons. The electrons are transferred into a cathode via an outer-circuit, and the protons are also transferred into the cathode through the polymer electrolyte membrane.
In addition, an oxidant is supplied to the cathode, and then the oxidant, the protons, and the electrons are reacted on catalysts of the cathode to produce electricity along with water.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.